1. The first 48 hours at home
Keep things calm and quiet. Your puppy has just left the only family they've ever known, so resist the urge to invite friends and neighbours over straight away — give them three or four days to settle first.
Set up a small 'puppy zone' with their crate, water, a few toys, and an easily wiped floor. Carry them outside to the toilet spot every hour or so, and especially after sleeping, eating, or playing.
Sit on the floor with them rather than picking them up constantly. Let them come to you. This builds trust from day one.